Reverse Defect Indicator for MPLS FM
OAMO3b NetworksUSAmishra.ashesh@outlook.comUSAmjethanandani@gmail.comCiena Corporation3939 North 1st StreetSan JoseCA95134USAankurpsaxena@gmail.comNetwork
Routing Working GroupInternet-DraftThis document describes extensions to the MPLS Fault Management
Operations, Administration, and Management (MPLS FM OAM) in RFC 6427 to support Remote Defect Indication
(RDI) functionality. Specifically, it describes a mechanism for
propagating MPLS FM OAM messages to the upstream Label Edge Router (LER)
in MPLS-TP bi-directional (associated and
co-routed) Label Switched Paths (LSPs).The MPLS Fault Management Operations, Administration, and Management
(MPLS FM OAM) in RFC 6427 describes a
method to identify faults in MPLS transport networks, and a protocol to
notify the upstream Label Edge Router (LER). However, in the case of
MPLS-TP bi-directional Label Switched
Paths (LSPs), the fault must be coordinated on both, the upstream LER
and the downstream LER (which is the upstream LER for the reverse
path).In typical scenario, the Bidirectional Forwarding Detection (BFD)
protocol, as described in RFC 5880,
detects the fault signaled by MPLS FM OAM on the upstream LER and
propagates the fault on the reverse LSP to the other MPLS-TP LSP LER.
This allows the two MPLS-TP LERs to coordinate failover to backup
LSPs.This document proposes a mechanism to achieve MPLS FM OAM fault
propagation on the MPLS-TP reverse LSP using a Reverse Defect Indicator
(RDI) MPLS FM OAM message. This allows fast fault coordination between
the bidirectional LSP end-points when the use of BFD is not
feasible.The functionality proposed for MPLS FM OAM RDI is achieved by adding
a RDI-flag in the MPLS Fault OAM message .where:L-Flag and R-Flag are as defined in RFC
6427.RDI-Flag: Reverse Defect Indication Flag. The RDI-Flag is clear in
the common MPLS FM OAM messages as defined in RFC
6427. The RDI-Flag is set to indicate that the message is MPLS FM
OAM RDI.
Forward LSP
+-------+ +-------+
+--> | LSR-1 | --X---> | LSR-2 | --+
| +-------+ Fault +-------+ AIS/LKR
| |
+-------+ --+ +--> +-------+
| LER-A | +-------+ | LER-B |
+-------+ Figure 1 depicts an associated bidirectional LSP with:Forward LSP (LER-A, LSR-1, LSR-2, LER-B)Reverse LSP (LER-B, LSR-3, LER-A)Scenario 1, Fault on LER-A: LSR-1 will detect a fault on the server
sub-layer and generate AIS/LKR message on the upstream link for
Forward LSP (towards LSR-2). LSR-2 will process the message and
forward it, unaltered, upstream to LER-B. LER-B will process the
message, set the RDI-Flag and forward it on the associated Reverse
LSP. Because the RDI-Flag is set, LSR-3 does not need to process the
message as the fault is not on the Reverse LSP and forwards it,
unaltered, towards LER-A. LER-A, if it receives the message (the fault
may only be on the forward LSP on LER-A) processes the message and
discard it (RDI-Flag set received on Reverse LSP indicates the fault
is on the Forward LSP, and vice-versa). When the fault clears, LSR-1
will issue new set of AIS/LKR messages to clear the previous fault
condition. This message is also propagated using the previous RDI
logic to coordinate fault clear on the Reverse LSP.Scenario 2, Link fault or LSR fault on Forward LSP: Same logic as
fault on LER-A.RDI is not a required mechanism in co-routed bidirectional LSPs as
MPLS LSx on either direction of the fault will generate MPLS FM OAM
messages and the fault is propagated to both LERs.None.No additional security impact because of addition of RDI-Flag in MPLS
FM OAM messages.